The present invention is directed to integrated circuits. More particularly, the invention provides systems and methods for reducing power consumption under light or no load conditions. Merely by way of example, the invention has been applied to a switch mode power converter under standby conditions. But it would be recognized that the invention has a much broader range of applicability.
Power converters have been widely used for consumer electronics such as portable devices. The power converters can convert electric power from one form to another. As an example, the electric power is transformed from alternate current (AC) to direct current (DC), from DC to AC, from AC to AC, or from DC to DC. Additionally, the power converters can also convert the electric power from one voltage level to another voltage level. Specifically, the power converters include linear converters and switch-mode converters. The switch-mode converters often use pulse-width-modulated (PWM) or pulse-frequency-modulated (PFM) mechanisms. The switch-mode converters usually are more efficient than the linear converters.
The power converters often must meet various international standards concerning energy savings, such as the Energy Star requirements and the Blue Angel requirements. Hence, the power converters usually need to have low power consumption and high power efficiency under light or no load conditions, such as under standby, suspended, or some other idle conditions.
FIG. 1 is a simplified conventional diagram showing a switch-mode power converter system with X-resistor and X-capacitor. The switch-mode power converter system 100 includes an X-resistor 110, an X-capacitor 120, input terminals 122 and 124, a switch-mode controller 130, diodes 152, 154, 156, and 158, a capacitor 160, a primary winding 172, a secondary winding 174, an auxiliary winding 176, and a switch 180. For example, the switch-mode controller 130 includes terminals 132, 134, 136, 138, and 139. In another example, the terminals 132, 134, 136, 138, and 139 are respectively the GND pin, the FB pin, the VCC pin, the GATE pin, and the CS pin.
To reduce power consumption of the converter system 100 under standby conditions, it often is important to lower the power consumption of the switch-mode controller 130. Additionally, the converter system 100 also includes other components, whose power consumption under standby conditions can become more significant as the power consumption of the switch-mode controller 130 is reduced. Therefore, the power consumption of these other components also need to be lowered in order to further reduce the power consumption of the switch-mode power converter system 100.
As shown in FIG. 1, the switch-mode power converter system 100 includes the X-capacitor 120 that is connected to the input terminals 122 and 124. The X-capacitor 120 often is used to address the issue of electromagnetic interference (EMI). But to maintain safety of the power converter system 100, the X-capacitor 120 needs to be discharged quickly so that the voltage across the X-capacitor 120 can drop below a predetermined threshold within 1 second after the input terminals 122 and 124 are disconnected from an AC power supply. To facilitate the discharge of the X-capacitor 120, the power converter system 100 also includes the X-resistor 110 that is connected to the X-capacitor 120 in parallel. But the X-resistor 110 would increase the power consumption of the power converter system 100 under standby conditions.
Hence it is highly desirable to improve the techniques of lowering power consumption under standby conditions.